The Effects of Prostaglandin E2 Treatment on the Secretory Function of Mare Corpus Luteum Depends on the Site of Application: An in vivo Study

Abstract

We examined the effect of prostaglandin (PG) E2 on the secretory function of equine corpus luteum (CL), according to the application site: intra-CL injection vs. an intrauterine (intra-U) administration. Moreover, the effect of intra-CL injection vs. intra-U administration of both luteotropic factors: PGE2 and human chorionic gonadotropin (hCG) as a positive control, on CL function was additionally compared. Mares were assigned to the groups (n = 6 per group): (1) an intra-CL saline injection (control); (2) an intra-CL injection of PGE2 (5 mg/ml); (3) an intra-CL injection of hCG (1,500 IU/ml); (4) an intra-U saline administration (control); (5) an intra-U administration of PGE2 (5 mg/5 ml); (6) an intra-U administration of hCG (1,500 IU/5 ml). Progesterone (P4) and PGE2 concentrations were measured in blood plasma samples collected at −2, −1, and 0 (pre-treatment), and at 1, 2, 3, 4, 6, 8, 10, 12, and 24 h after treatments. Moreover, effects of different doses of PGE2 application on the concentration of total PGF2α (PGF2α and its main metabolite 13,14-dihydro-15-keto-prostaglandin F2α– PGFM) was determined. The time point of PGE2, hCG, or saline administration was defined as hour “0” of the experiment. An intra-CL injection of PGE2 increased P4 and PGE2 concentrations between 3 and 4 h or at 3 and 12 h, respectively (p < 0.05). While intra-U administration of PGE2 elevated P4 concentrations between 8 and 24 h, PGE2 was upregulated at 1 h and between 3 and 4 h (p < 0.05). An intra-CL injection of hCG increased P4 concentrations at 1, 6, and 12 h (p < 0.05), while its intra-U administration enhanced P4 and PGE2 concentrations between 1 and 12 h or at 3 h and between 6 and 10 h, respectively (p < 0.05). An application of PGE2, dependently on the dose, supports equine CL function, regardless of the application site, consequently leading to differences in both P4 and PGE2 concentrations in blood plasma.

Characterization of serum and tissue oxytocinase and tissue oxytocin in the pregnant and non-pregnant mare

“…The decrease in LNPEP increased the sensitivity of this cells to OXT, which then resulted in an increased secretion of PGE2 35 , which is luteotrophic. The luteotrophic action of PGE was shown by direct injection of luteal tissue with PGE and high dose intrauterine administration of PGE 39 . It is unknown if progesterone has an effect on LNPEP at the tissue level, and therefore promotes PGE2 secretion for luteal maintenance during early pregnancy.…”

Serum Cytokine Reactions during Pregnancy in Healthy Mares

“…There are several aspects which suggest that horses may be a good model for reproductive studies in humans. The nonsurgical recovery of early-stage embryos and conceptuses, as well as the isolation of pure trophoblast cell populations, are possible because of the horse conceptus' unique structure and physiology, and such an outcome is not possible in other model organisms [8][9][10][11][12]. However, it appears that horse and human pregnancies are similar in many aspects; more study is needed.…”